Tension control devices for regulating the withdrawal of filamentary material from a spool have been known for a number of years. Filamentary materials include single- and multiple-strand fibers produced in long lengths and conveniently wound on spools to facilitate handling. Filamentary materials are variously made of natural or synthetic fibers, glass, or metal. Such materials in the form of filaments are commonly utilized as reinforcing members for plastic or elastomeric compounds, or the materials themselves may be fabricated into integral items, as is done in the textile industry. In most applications, it is advantageous to withdraw the filamentary material from the spool at or near the location it is being used in a manufacturing process. To facilitate such withdrawal, a spool is customarily mounted on a spindle, which may be mounted on a creel assembly as one of a plurality of spindles carrying spools, which permit the spools to rotate as the filament is withdrawn, normally simultaneously from a plurality of spools.
The payout of the filamentary material from the spool may be at a high linear velocity, thereby imparting substantial momentum to the spool and related spindle. As a result, it is necessary to dissipate force rapidly in the event the filamentary material breaks or take-up force suddenly decreases or stops. In such situation, filamentary material continues to be payed out more rapidly than it is needed or desired until rotation of the spool can be appropriately slowed or retarded. The presence of excessive slack in the filamentary material can produce twisting of the filamentary material or interference with associated machinery or other spools, particularly where a great number of spools are continuously operating in close proximity, as when mounted on a creel assembly.
In order to compensate for excessive payout of filamentary material in the event of a break in the filamentary material or a sudden decrease in the take-up, braking devices have been developed for use with creels. In such devices, as the tension decreases, producing slack in the filamentary material, a breaking force is applied to slow the rotation of the spool. Features required in such breaking or tension control devices are the capability of varying the amount of tension in the filamentary material; a simple, single adjustment to provide a desired tension; the absence of the necessity to adjust tension as the spool is emptied, and a configuration that eliminates undesirable hunting or loping in the form of periodic variations in tension about a desired tension setting. These requirements have been satisfied by a tension control device for spools pursuant to Applicant's Assignee's U.S. Pat. No. 3,899,143.
In addition to the above-described instances where tension in the filamentary material suddenly decreases, there are also instances in the operation of spool payout where the tension suddenly greatly increases. Such increases in tension may be caused by a snag in the filamentary material at the spool, an overlap or other miswinding of the filamentary material, mechanical interference with the rotation of the spool, or other reasons. As can be appreciated, a snag or the like can provide an abrupt and severe tension increase in the filamentary material exceeding the design range of the tension controller. In the event of the usage of a roller paralleling the spool axis mounted on a control arm as an operative element of a tension control device, such a tension overload in the filamentary material can cause the control arm roller to put a bending moment or torsional load on the control arm, which can break or permanently deform the control arm and/or the roller, thereby rendering the tension control device inoperable until replacement parts are obtained and installed. Where payout velocities of the filamentary material are extremely high and the filamentary material is in the form of steel cords, it is apparent that sudden tension overloads can readily be destructive of even a control arm configuration designed to withstand several times the forces encountered in the normal working range of the tension controller.